The Maine governor and establishment pick to challenge GOP Sen. Susan Collins said she wants to keep the Senate's 60-vote requirement for most legislation.

Maine Democratic Gov. Janet Mills announced that she will be running for U.S. Senate in an effort to unseat Republican Sen. Susan Collins.

Maine's Senate race will be one of the most closely watched races in next year's midterms. Mills will first square off with fellow Democrat Graham Platner.

Many leading progressive senators are sitting on the sidelines despite their leaders backing Maine Gov. Janet Mills, who jumped into the race this week.

The Maine governor and establishment pick to challenge GOP Sen. Susan Collins said she wants to keep the Senate's 60-vote requirement for most legislation.